1. Field of the Invention
The present invention relates to a gas sensor and a gas sensor system that are exposed to a humid condition. Also, the present invention relates to a controlling method of the gas sensor system.
2. Description of Relevant Art
Generally, in a fuel cell which adopts solid polymer electrolyte membrane, a fuel cell stack is configured by stacking a plurality of single cells, which is obtained by sandwiching a membrane electrode assembly by a pair of separators. Here, a membrane electrode assembly is obtained by sandwiching a solid polymer electrolyte membrane, from both sides thereof, by a fuel electrode and an oxygen electrode.
In this fuel cell, hydrogen is supplied, as fuel, to the fuel electrode and air is supplied, as oxidant, to the oxygen electrode. Then, hydrogen ion caused by a catalytic reaction at the fuel electrode passes through the solid polymer electrolyte membrane and reaches to the oxygen electrode. Thus, electric power is generated through an electrochemical reaction between hydrogen ion and oxygen.
In this kind of fuel cell adopting a s solid polymer electrolyte membrane, conventionally, a gas sensor (hydrogen sensor) is provided at an exhaust line of oxygen electrode-side, and a technique, which detects the leakage into the oxygen electrode side of hydrogen through the solid polymer electrolyte membrane from the fuel electrode side using this sensor, has been discovered (see Japanese unexamined patent publications No. H06-223850 and No. 2004-61244).
In these conventional techniques, the gas sensor is disposed on the exhaust line so that a hydrogen intake of the gas sensor is directed to a downside in a vertical direction. Thus, since specific gravity of hydrogen is small, the introducing of hydrogen into the gas sensor is surely achieved.
In these conventional techniques, droplet of water contained in the gas is removed by a water-repellent filter which is provided to the hydrogen inlet, to prevent the adhesion of the droplet of water to a gas detector in the hydrogen sensor.
In these conventional techniques, however, a humid off-gas discharged from the fuel cell is introduced into the gas sensor regardless of the power generation of the fuel cell and the stop of the power generation. In this case, the corrosion (deterioration etc) of the detector may be caused due to the droplet of water that adheres to the gas detector for hydrogen (target gas). Thus, the occurrence of the trouble on the gas sensor is caused sometimes.
Therefore, there have been required the gas sensor and gas sensor system which is resistant to a trouble.